In late years, a transparent organic polymer material has been used as a transparent material in place of an inorganic glass. When such a material is used, for example, for a resin for an optical, there has been demanded such a resin having required general properties such as transparency, thermal properties, mechanical properties and the like, while attaining a high refractive index.
A technique concerning such a resin has been disclosed in Patent Document 1. In the Document, a metal-containing thietane compound has been disclosed.    Patent Document 1: International Publication Pamphlet No. 2005/095490    Patent Document 2: Japanese Patent Laid-open No. 2003-327583    Patent Document 3: International Publication Pamphlet No. 2006/054615